Stress Fracture

BASICS

Definition:
Overuse injury caused by cumulative microdamage from repetitive bone loading.
Types:
- Fatigue fracture: abnormal repetitive stress on normal bone (e.g., athletes, new military recruits).
- Insufficiency fracture: normal stress on abnormal bone (e.g., osteoporosis).
- Combination fracture: abnormal stress on abnormal bone (e.g., female athlete triad).
Common sites: tibia/fibula (most common), metatarsals, navicular, femoral neck, pars interarticularis.
High-risk sites: femoral neck, anterior tibial diaphysis, sesamoids, pars interarticularis (L4, L5), 5th metatarsal (metaphyseal-diaphyseal junction), proximal 2nd metatarsal, medial malleolus, tarsal navicular, patella, talar neck.

Incidence: Highest in ages 15–27 years; females > males.
Prevalence: Up to 20% of visits to sports medicine/ortho clinics; lifetime risk in athletes ≈10%.
Military: 6.9% of males, 21% of females.

Bone undergoes constant remodeling in response to stress.
Repetitive loading → microfractures accumulate → imbalance between resorption and formation.
Untreated microdamage → progression to stress fracture.

Intrinsic:
Female sex (2.3x risk)
Female athlete triad
Small tibial width
Delayed menarche/amenorrhea/irregular menses
History of stress fracture or osteoporosis
Low BMI (<19 kg/m²)
Skeletal malalignment (pes cavus/planus, leg length discrepancy, etc.)
Biomechanical: increased vertical loading (heel-to-toe running)
Extrinsic:
High-risk sports (track/field, cross country)
Running >20 miles/week or >5 hours/day
Poor nutrition, eating disorders, low vitamin D
Rapid increases in training volume/intensity
Improper footwear/hard surfaces
Inadequate rest/recovery, muscle fatigue
Smoking, high alcohol intake
Meds: steroids, anticonvulsants, antidepressants, DMPA, methotrexate, antiretrovirals, cannabis, >5 years bisphosphonates

Insidious onset, vague pain worsened by activity, progressing to pain at rest if untreated.
Recent changes in training or equipment.
Female athletes: ask about menstrual history.
Dietary history, prior stress fractures.

Labs: Only if suspecting underlying metabolic disease or female athlete triad.
Imaging:
X-ray: first line but often negative early (findings after 2–8 weeks).
MRI: gold standard—early detection, high sensitivity/specificity.
Bone scan: sensitive but not specific; early detection.
CT: useful for bony detail, chronic/occult fracture, and equivocal MRI.
US: rarely used.
Radiographic classification:
Grade I: periosteal edema only, no fracture line
Grade II: pain, marrow edema, no fracture line
Grade III: nondisplaced fracture line present
Grade IV: displaced fracture >2 mm
Grade V: nonunion

First Line:
Calcium (up to 2 g/day), vitamin D (800–4,000 IU/day)
Acetaminophen for pain
NSAIDs with caution—may delay healing
Second Line:
Bisphosphonates (IV pamidronate/ibandronate) or teriparatide in refractory cases
OCPs do not restore bone density in athletes

High-risk fracture sites, non-healing, or nonunion
Failure to improve with standard care
Consider multidisciplinary approach (team physician, nutritionist, PT, orthopedics, endocrinology)

High suspicion required—x-rays often initially negative.
Always address the female athlete triad or metabolic disease if suspected.
Gradually increase training, avoid sudden high-impact loads.
High-risk fractures = immobilization/non-weight-bearing and may need surgery.
All stress fractures need proper rehab and risk factor correction to prevent recurrence.